1. Field of the Invention
The present invention relates to a medical instrument having an insertion section adapted to be inserted into a living body, such as an ultrasonic treatment apparatus, an endoscope, treatment means, or a resectosheath for guiding the endoscope or treatment means into the body cavity.
2. Description of the Related Art
Improved endoscope apparatuses are widely used in recent years. In these apparatuses, an elongated insertion section is inserted into a living body to be used for the observation of internal organs in the body cavity, and treatment means for various treatments can be inserted as required into treatment means channels.
In inserting the treatment means or one such endoscope apparatus into the body cavity, an elongated hollow guide tube is inserted in advance into the living body, and the treatment means or the endoscope apparatus is inserted into the body cavity, for the treatment and observation therein by utilizing the guide tube.
The endoscope apparatuses of this type include, for example, high-frequency endoscope apparatuses which are used to resect tissues in the prostate, uterus, ureter, renal pelvis, etc. An example of these apparatuses is disclosed in Published Unexamined Japanese Utility Model Application No. 60-149616. In a resectoscope apparatus described in this application, an electrode for resection, along with an insertion section, is inserted through the urethra into the urinary bladder, and a high-frequency current is supplied to the electrode, whereby the prostate can be resected.
In general, a resectoscope apparatus comprises a hollow sheath adapted to be inserted into the body cavity, an operating section with a slider removably attached to the rear end of the sheath, and an observation scope removably attached to the operating section from the rear end side thereof. In this arrangement, an electrode for resecting tissue in the body cavity can be projected or retreated from the distal end of the sheath by means of the slider. The distal end of this electrode, which is bifurcated to form a loop, is housed in a sheath insertion section, and the proximal end portion of the electrode is fixedly connected to an electric contact of the slider.
In this resectoscope apparatus, the slider is moved back and forth while supplying a high-frequency current to the electrode which is held against an affected part. Thereupon, the electrode moves back and forth, so that the affected part can be resected or coagulated.
Generally, a sheath of a resectoscope apparatus or the like is composed of an insertion section, in the form of an elongated hollow tubular member adapted to be inserted into the body cavity, and a body section having a connecting portion continuous with the proximal side of the insertion section. Since the insertion section of the sheath is expected to be inserted into the body cavity of a patient, its outside diameter must be minimized in order to reduce invasion on the body cavity side.
Meanwhile, a scope for the observation of the affected part must be inserted into the sheath insertion section, and its diameter should be as large as possible for better observation performance. A perfusate is fed into the body cavity through the inside of the sheath insertion section for use as a duct. In order to secure a clear view field, a satisfactory amount of perfusate must be supplied, so that the greatest possible passage for the perfusate should be formed.
Under these circumstances, it is necessary to maximize the inside diameter of the sheath insertion section and minimize the outside diameter thereof. Preferably, therefore, the wall thickness of the sheath insertion section to be inserted into the body cavity should be minimized. At the same time, the insertion section must have a mechanical strength high enough to stand a crushing force acting thereon and a bending force produced when it is inserted into the body cavity.
Since the distal end portion of the sheath insertion section is touched by the looped electrode for resecting or coagulating the affected part by means of the high-frequency current, it should be formed of a material which has a good insulating property against the high-frequency current and a heat resistance of 300.degree. C. or more to stand heat produced when the affected part is resected or coagulated.
In consideration of these circumstances, the conventional sheath insertion section is formed of a metallic pipe, such as a stainless-steel pipe, which can enjoy a high mechanical strength despite its thin wall. A beak, which is formed of epoxy resin improved in heat resistance by being mixed with glass or ceramic fibers, is fitted in the distal end portion of the sheath insertion section, and fixed by adhesive bonding or the like, whereby the distal end portion is insulated from the looped portion of the electrode.
With use of this arrangement, the insulation between the looped portion of the electrode and the distal end portion of the sheath insertion section can be maintained for certain. As mentioned before, however, the outside diameter of the sheath must be minimized, so that an insulating coating of a good thickness cannot be applied to the sheath insertion section. Although the sheath insertion section can be fully insulated from a DC current, therefore, it may possibly be subjected to a small leakage of the high-frequency current (usually hundreds of kilohertzes). In such a case, the high-frequency current may leak into the body cavity of the patient, thereby causing a burn or electric shock to the patient's body.
Since the metallic sheath insertion section and the beak are separate components, moreover, the beak may possibly fall off in the body cavity as the insertion section is inserted into the cavity.
In order to eliminate these drawbacks, some sheaths have an insertion section which is formed of a thin-walled cylinder of glass fiber cloth impregnated with epoxy resin. With use of these sheaths, there is no possibility of the beak falling off or a current leaking from the sheath insertion section into the body cavity, indeed. Since the core of these sheaths is made of glass fiber cloth, however, its wall is inevitably thick. As compared with about 0.5 mm for the wall thickness of a metallic pipe, such as a stainless-steel pipe, a wall thickness of 0.7 mm or more is required of the glass-cloth sheaths. Thus, the outside diameter of the insertion section is inevitably large.
If he insertion section has a large outside diameter, invasion on the body cavity side is substantial. It is very troublesome and time-consuming, moreover, to prepare the glass fiber cloth, impregnate it with the epoxy resin, and form the resulting structure into a cylinder, so that the insertion section is expensive.
There are very few electrically insulating thermoplastic resins which have a heat resistance of 300.degree. C. or more. They include, for example, polyether-ether-ketone (PEEK) and polyamide-imide (PAI). These heat-resistant thermoplastic resins are too poor in melt-flow characteristics to be used for the manufacture of a long thin-walled pipe (about 20 cm long and 0.5 mm thick) by injection molding or extrusion molding. It is difficult, therefore, to use these resins as materials for the sheath.
The above is a description of the sheath of the resectoscope apparatus which is adapted to be inserted into the urinary bladder per urethra for some treatments, such as the resection of the prostate. The aforementioned problems are not, however, peculiar to the sheath of the resectoscope, and lie also in the insertion sections of other medical instruments. These instruments include, for example, the sheath of a cystourethroscope apparatus and a thoracal mantle tube in which a guide tube called a thoracal is stuck into the abdominal wall, and a scope or treatment means is inserted into the thoracal to enable the observation of internal organs inside the abdominal wall or high-frequency treatment.